Swing tongue, pull-type crop harvesters have gained widespread acceptance with farming personnel due to their capability to be controlled by the tractor operator to effectively steer or navigate through a variety of turns and maneuvers in a field with standing crops. With respect to center pivot swing tongue harvesters wherein the draw bar or tongue is pivotably connected adjacent the transverse center of the harvester, the machine has the ability to cut and/or condition crops as it is towed back and forth by the tractor across a field with the harvester swinging from one side of the tractor to the other during alternate runs. Harvesters of this type typically include a wheeled frame to which the tongue is connected, and a harvesting head pivotably mounted to the frame for movement about a horizontal axis between raised and lowered positions.
Swinging the crop harvester laterally from side-to-side behind the tractor, however, causes difficulties in the transmission of driving power from a power take-off shaft on the tractor to the cutting and conditioning components of the machine. One crop harvester of this type is disclosed in U.S. Pat. No. 4,858,418 issued Aug. 22, 1989. This patent discloses a mowing machine having an undercarriage frame and a crossbeam to which a plurality of cutting tools are mounted for rotation about vertical axes. Cutter blades are connected to the lower ends of the cutting tools. The cutting machine is connected to the tractor by means of a pivotable tractor hitch and the cutting tools are driven by a drive line interconnecting a power take-off shaft of the towing tractor and a gear box on the crossbeam. The drive line includes a fixed position shaft segment and a universally jointed telescopic drive shaft assembly. The gear box is pivotally connected on a middle part of the crossbeam and the drive line is connected with the gear box by means of a support joint having forked parts pivotally interconnected on a horizontal axis. In this arrangement, the forces necessary to steer or pivot the gear box are transmitted through the drive line to the forked support joint between the gear box and the drive line.
Another example of a swing-type crop harvester is disclosed in U.S. Pat. No. 5,272,859 issued Dec. 28, 1993. In this patent, a drive line from the power takeoff shaft of the tractor extends along the tongue and is supported in underslung relationship so that the rear end of the drive line is coupled with the input shaft of the gear box which extends fore and aft. A conventional drive line shield surrounds the drive line to prevent entry of contaminants into the telescoping sections and to prevent accidental contact with the drive line. When the tongue is swung back and forth to reposition the harvesting portion of the machine, a telescoping section of the drive line between a supporting point on the tongue and the connection with the gear box telescopically extends and retracts to accommodate the different axes of rotation of the tongue of the gear box. A telescoping steering linkage is connected between the tongue and the gear box to steer or pivot the gear box as the tongue is swung. This arrangement relieves steering forces on the drive line but adds to the time and cost of assembly due to the separate gear box steering mechanism.
Attempts have been made by the prior art to address the problems in transmitting power from the tractor to the cutting and conditioning components of the harvester by employing different structures to provide input power from the drive line to the gear box and to pivot or steer the gear box. It is an object of the present invention to provide a mechanical drive line connection and gear box steering structure which is capable of satisfying the power requirements of the harvester while minimizing the torsional loading on the telescopic drive line connection at its connection to the gear box. It is a further object of the invention to provide a power input and gear box steering structure which is simple in its design and construction. A further object of the invention is to provide a power input and gear box steering structure which does not entail any significant increase in cost of components or assembly over prior art constructions.